The process of shuttering consists of exposing an image sensor to light at a rate equal to (or faster than) a frame rate. The goal of this process is to reduce blurring effects from motion within an image frame.
There are several different types of shuttering including rolling shuttering and global shuttering. A rolling shutter exists where a line of pixels, or a group of several lines of pixels, is read out while other lines in the image sensor are exposed to image light. Readout times for rolling shutter image sensors vary depending on frame rate and architecture, but can be as high as several hundred microseconds. Accordingly, due to the delay between reading each line of pixels, moving image subjects can cause optical distortion and blur within the image.
A global shutter, unlike a rolling shutter, exposes all photodiodes in the image sensor at the same time. This results in little or no image blur because there is no delay between integration of individual pixel lines during image acquisition. However, global shutters generally require an additional pixel storage element which allows the pixels to store previously acquired image charge to be read out while the next image frame is captured. This additional storage element generally enlarges the footprint of individual pixels on a wafer, and can be a source of problems such as light absorption, cross talk, etc.
Corresponding reference characters indicate corresponding components throughout the several views of the drawings. Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.